(1) Field of the Invention
This invention relates to non-crystallizing rosin. More particularly, this invention provides a rosin stabilized against crystallization by the addition of a hard rosin ester.
For most rosin uses, a product not having a tendency to crystallize is highly desirable. Crystalline rosin is more difficult to saponify, easily crystallizes out of solution during the preparation of varnishes and above all presents serious handling difficulties.
(2) The Prior Art
Prolonged heating or injections of steam with the addition of caustic are used to render crystalline rosin useful. This treatment is costly and leaves rosin with a darker color. Other methods used to reduce or prevent crystallization include heat treatment, partial neutralization with sodium hydroxide, polymerization, and reaction with formaldehyde or dienophiles. These methods, based mainly on changes in the rosin composition, involve alterations in the structure and chemical properties of the rosin acid molecules.
In U.S. Pat. No. 2,572,035 Jordan et al. partially esterify rosin with pentaerythritol to the extent that the acid number is reduced 25% to 50% and a liquid product is obtained. Barthel in U.S. Pat. No. 2,576,094 makes a non-crystallizing rosin suitable for making liquid rosin size, by heating rosin with phenothiazine. In U.S. Pat. No. 2,776,275 Strazdins describes stabilizing rosin against crystallization with a small amount of the condensation product of rosin with a saligenin. Eckhardt in U.S. Pat. No. 2,659,718 describes treatment of fatty acid-rosin mixtures to inhibit crystallization using alcohols and formaldehyde. Yet another method for preventing crystallization of rosin is described by Strizhakov, "Prevention of Rosin Crystallization," Gidroliznaya i Lesokhimicheskaya Promyshlennost' No. 7:9-10 (1975) and involves the addition to a rosin melt or to an oleoresin of 5% to 10% rosin anhyride or the treatment of rosin with acetic anhydride. Although the method of Strizhakov, like some of the other methods, is effective, it undesirably results in a substantial softening of the rosin.
It is, therefore, the general object of this invention to provide a non-crystallizing rosin with essentially the same physical properties as the starting rosin.
Another object of this invention is to provide a hard, homogeneous, readily liquifiable rosin in which a rosin ester has been added to a rosin melt.
Yet another object of this invention is to provide a method for making a hard, non-crystallizing rosin.
Other objects, features and advantages of this invention will be evident from the following detailed description of the invention.